Mobilization of retinol from cultured rat liver stellate cells does not require protein secretion

Vitamin A is mobilized from the liver stellate cells (LSCs) by a mechanism in which the involvement of a protein is still controversial. We adressed this question on primary cultures of rat LSCs, with two different approaches. Firstly, culture media of LSCs were concentrated by lyophilization and dialysis or by centrifugation on a 5 kDa cut off membrane, incubated with tritiated retinol and submitted to a non-denaturating electrophoresis, toghether with standard preparations. Scintillation counting of gel slices did not detect the presence of any protein able to bind retinol. Secondly, we showed that, although brefeldin A blocked the secretion of proteins from LSCs (checked on fibronectin), it did not modify the secretion of free retinol from the LSCs into the medium. We conclude that the mobilization of retinol from LSCs does not require protein secretion.